Image processing is often heard of in photography and movies. The scanner is an indispensable part of this technology. There are two kinds of scanner: one is reflection-mode, and the other is transmission-mode. The reflection scanner is used for scanning an opaque article such as common papers, while the transmission scanner is used for scanning a transparent article such as transparencies, and is not as popular as the reflection scanner.
A side view of a conventional transmission scanner is shown in FIG. 1(a). The scanner has an upper housing 1 and a lower housing 2, and is used for scanning a transparency 4. A transmissive light source 13 electrically connected to a socket 14 provides an optical signal for the transparency 4 to generate a scan optical signal. In the moving carriage 3 is an image-picking device used for processing the generated scan optical signal. The image-picking device includes a mirror 31, a charge coupled device 32, and a lens set 33. The scan optical signal is transmitted to the charge coupled device 32 by the mirror 31, then the charge coupled device 32 converts the scan optical signal into an electronic signal to form digital information later, while the lens set 33 is used for focusing the scanned signal in order to shorten the length of the moving carriage 3. According to the operating principle, the transmissive light source 13 must be moved with the moving carriage 3 synchronously in order to scan the whole transparency 4. Therefore, the driving device is needed to move the transmissive light source 13 in the upper housing 11 and the moving carriage 3 in the lower housing 2. The motors 111 and 21 drive the corresponding belts 12 and 22 to circulate around the corresponding gears 15 and 23 and the corresponding motors 11 and 21. The transmissive light source 13 and the moving carriage 3 are respectively moved between corresponding gears 15 and 23 and corresponding motors 11 and 21 by corresponding belts 12 and 22. The conventional transmission scanner must be equipped with two sets of driving device which not only occupy more volume but also require higher production cost. Certainly, the complexity of the circuits can not be ignored.
Since the transmission scanner is less popular than the reflection scanner, a scanner with both the transmission-mode function and the reflection-mode function seems more economical. A side view of a conventional scanner with both the transmission-mode function and the reflection-mode function is shown in FIG. 1(b). The devices marked with the same number as shown in FIG. 1(a) are with similar function. The additional reflective light source 34 electrically connected to the corresponding socket 35 is mounted in the moving carriage 3 to provide an optical signal. If the scanned article 4 is a transparent article such as a transparency, the transmissive light source 13 is lit to provide an optical signal for the transparency 4, and a scan optical signal is thus generated. The scan optical signal is reflected by the mirror 31, focused by the lens set 33, and converted into an electronic signal by the charge coupled device 32 in sequence. If the scanned article 4 is an opaque article such as a piece of paper, the reflective light source 34 is lit to provide an optical signal for the piece of paper 4, then a scanned optical is generated, reflected, focused, and converted into an electronic signal as stated above. The transmissive light source 13 is transferred by a driving device which includes the motor 11, the belt 12, and the gear 15 to scan the whole transparency 4, while the reflective light source 34 is mounted in the moving carriage 3 transferred by another driving device which includes the motor 21, the belt 22, and the gear 23 to scan the whole paper 4. Although the scanner serves more applications, the trouble of high production cost and complex circuit due to the two sets of driving device still exists.
A scanner with both the transmission-mode function and the reflection-mode function according to another prior art introduces a light-distributing sheet instead of the transmissive light source and the driving device mounted in the upper housing. The light-distribution sheet is a smooth-faced sheet which has two fluorescent tubes on the two sides of the smooth-faced sheet. The light is dispersed under the light-distribution sheet which covers the whole scanned article and does not need moving. The light-distribution sheet suggested by the prior art, however, can not distribute light homogeneously, so the scanning quality is affected. Another disadvantage of this scanner is the high cost of the light-distribution sheet. Thus, a better scanner with lower cost is in great hope.